In this post we introduce simple and flexible, regulated low voltage power supply unit. This power supply has provision for 4 outputs such as 1.5V, 1.8V, 2.5V and 3.3V. We mainly build this low voltage power supply unit to test (and power-up) low voltage MCUs, CPLDs and radio receivers. For this power supply we choose 1.8V, 2.5V and 3.3V to get it compatible with most of the LVTTL/LVCMOS devices. Other than that, we include 1.5V because there are several analog ICs are available for that voltage level.

This power supply unit is based on LM1117/AMS1117 voltage regulator series and for this design we use AMS1117-1.5, AMS111-1.8, AMS1117-2.5 and AMS1117-3.3 fixed voltage regulators. Except to above regulators this board can be use with AMS1117-2.85 and AMS1117-5.0 regulators.

In our prototype we use center-tapped 6V (1A) step down transformer with this power supply unit. All the wiring diagrams to transformer and rotary switch are provided with the schematic.

Final view of low voltage power supply unit.
Final view of low voltage power supply unit.

The given PCB design for this power supply unit is based on SOT-223 (SMD) version of voltage regulators. Even though it use SMD components this PCB can build with single side PCB. Dimension of the PCB is set to 89mm × 69mm.

In our prototype we got following voltages with this PSU (Temperature: 31°C):

Position

Expected voltage

Output voltage
1

1.5V

1.49V
2

1.8V

1.80V
3

2.5V

2.49V
4

3.3V

3.29V

Project Related Downloads


PCB designs and schematics of low voltage power supply unit.

References


LM1117 - 1A Low dropout voltage regulator.